1. Field of the Invention
The present invention relates to an X-ray computerized tomographic apparatus which reconstructs an image under ECG gated reconstruction.
2. Description of the Related Art
An X-ray computerized tomographic apparatus provides information on a patient, in terms of an image on the basis of the intensity of X-rays transmitted through the patient. It plays important roles in a large number of medical services including the diagnoses, remedies and operation plans of diseases.
Cardiac examinations require high temporal resolutions. The requirement is chiefly coped with by adopting ECG gated reconstruction, or shortening a time period per revolution of an X-ray tube (heightening a rotational scan speed). In the ECG gated reconstruction, projection data corresponding to, for example, 3 heart beats are acquired. Data of close beat phases are extracted from the respective heart beats, so as to obtain a complete set of data for 360° or 180°+α (α:fan angle) as are necessary for image reconstruction. An image is reconstructed from the completed data.
JP-A-2003-164446 discloses a technique which obtains a complete set of data for 180°+α by excluding irregular heart beats, thereby to relieve artifacts. In this technique, a slice start position and a slice end position are determined beforehand, and a scan is ended at the point of time at which a scan position has reached the slice end position. Subsequently, the data for 180°+α are completed by excluding the data of the irregular heart beats from among data acquired from the slice start position to the slice end position which are previously set. Therefore, the number of heart beats from which the data for 180°+α have been collected can be settled only after the scan. Accordingly, a situation can occur where an intended temporal resolution has not been attained.